This disclosure describes a novel method for producing high-quality images of remote target scenes. The images are constructed from RF measurements made in the focal plane of a suitable imaging system. Mathematical processing of the measurements using Fourier transform techniques is used to compensate for the limitations of practical imaging systems and provide greatly enhanced resolution
The method visualizes a target scene consisting of a multitude of RF sources, all of the same frequency but having different amplitudes and phases. Alternatively, the target scene may consist of a multitude of reflectors or scatterers, all illuminated by a single source of single-frequency RF energy. The method further visualizes a lens or more general optical imaging system that focuses RF energy from the scene onto its focal plane. The amplitude and phase of this RF energy are measured at a number of points in the focal plane by an array of sensors, a single sensor that scans across the focal plane, or a combination of these techniques. An image of the original target scene is then reconstructed from these measurements.
If the imaging optics were perfect in a system as just described, the remote scene would be represented directly by the measurements made in the focal plane. In a practical system, however, the imaging optics and its associated aperture introduce diffraction effects and other aberrations which limit the usefulness of the raw image. It is the purpose of the method described herein to overcome these limitations to the greatest extent practical. This is done by performing certain mathematical operations on the, basic focal-plane measurements as part of the process of reconstructing the image. These operations utilize the techniques of Fourier transform theory and analysis.